Current medical technology includes a variety of devices that can be implanted in the body. One family of implantable devices are constructed of polymeric materials having desirable physical properties, including the ability to polymerize in situ, the ability to absorb water, biodegradability etc. Depending on the application, it may further be desirable to provide an implantable device with surface properties that enhance cell adhesion. To date, however, an implantable material having properties that are optimal for certain applications has not been known.
Polymeric materials carrying cationic groups have been investigated for possible applications as cell carriers, blood compatible coating, anti-microbial materials, and as drug delivery systems. It has been reported that cationic modifications of polymeric materials tend to enhance cell adhesion because phospholipids and proteoglycans that are present on cell surfaces are negatively charged.
Mori et al. have demonstrated that surface modification of medical devices with cationic polymers could immobilize negatively charged heparin, thus reducing the surface thrombogenecity due to a gradual release of heparin.(2) Augusta et al. have reported that sucrose methacrylate hydrogels modified with quaternary ammonium salts exhibited a bactericidal effect on gram positive and gram negative bacteria. (3) Applications of polycations such as poly(spermine), poly(L-lysine), and poly(2-dimethylaminoethyl methacrylate) for local gene delivery have been summarized in recent reviews. (4,5)
In addition, various hydrogels have been investigated for their applications as cell carriers to regenerate tissues. Biodegradability and biocompatiblility important parameters in the design of hydrogel materials for tissue engineering applications. However, the cationic hydrogels of previous investigations have been non-degradable.
Poly(propylene fumarate-co-ethylene glycol) (P(PF-co-EG)) has been proposed as an injectable biodegradable polyester. The fumarate double bond enables the copolymer cross-linking. The minimal temperature increase exhibited by P(PF-co-EG) during cross-linking in the presence of water makes P(PF-co-EG) suitable for use as a cell carrier. It has been shown that a hydrogel consisting of P(PF-co-EG) and N-vinylpyrrolidone exhibits bulk degradation. When the P(PF-co-EG) hydrogel was subcutaneously implanted in rats, it elicited a minimal inflammation response. (11-13)
However, when the hydrophilicity of a P(PF-co-EG) hydrogel was increased by increasing the molar ratio of the ethylene glycol repeating unit to the propylene fumarate repeating unit of the P(PF-co-EG) copolymers, cell adhesion to the surface of the hydrogels decreased. (15) Furthermore, hydrogel modifiers such as cationic monomers have been limited by their possible toxicity. Therefore, there remains a need for a hydrogel having the desired physical traits, including hydrophilicity and enhanced cell adhesion.